The Geant4Simulation Study Of The Dark Matter Detector

The dark matter is one of the major topics in contemporary physics. The cosmology requires the existence of the dark matter and its collisionlessness and low temperature. Based on this assumption, a number of dark matter candidates are proposed in particle physics besides the standard model. Among them, the supersymmetric model (SUSY) with weakly interacting massive particles (WIMPs) is the most popular candidate because they are detectable. The WIMPs does not participate in the electromagnetic and strong interactions, but only weak interaction. They have a relatively large mass with a high speed, and they can penetrate the detector shielding and collide with the atoms inside the detector. As a result, tens of keV energy can be propagated to the atoms, which leads to the atomic ionization, excitation or lattice vibration, and so that they can be detected. Experimental detection of WIMPs has a very important contribution to the development of new physics.In the direct detection of dark matter experiments, the interaction rate is very low, thus excluding the background is the key to improving the signal resolution. Based on this, we study the characteristics of the signals and the recoil nucleus electrical signal in Csl (Na) crystal detector.According to the integral value of their screening thresholds to exclude electronic signals, the result can reduce misjudgment rate and accuracy can be up to80%. Further experiments found that appropriate temperature can reduce the detection threshold while improving the background rejection capability.The experiment results show that the signal has the best resolution at about-100℃.Based on Geant4, this thesis simulates the dark matter central detector, including its geometry and simulations of shielding layer material. The thesis contrasts theand light collection and energy distribution of the different sized cylindrical crystals. It finds out that the small crystals can collect more photons than large crystals. Besides, it is easier to make small crystals.So the central detector selects small crystals with a diameter of10cm and height of50cm.In addition, this paper simulates background cases of the cosmic ray muon from the selection of shielding materials. Background cases are obtained by comparison among different anti-coincidence and low walls of different materials. The total base number of muon when anti-coincidence is made of the inner water is less than that when it is made of the double-layer water, so the double-layer water is used as anti-coincidence in the experiment. The total base number of muon when low wall is made of stainless steel tank is less than that when it is made of polyethylene tetrafluoride, so stainless steel tank is used as low temperature wall in the experiment. The great science project of dark matter’ s direct detection is going ahead smoothly right now. The result of this paper’ s research optimizes the design parameters of detectors as well as provides a reference for the shield design of dark matter’s detector.